Liquid-Phase Capillary Etching of Poly(Dimethylsiloxane) Microchannels With Tetra-n-Butylammonium Fluoride

Easy fabricability, along with other unique properties, has made poly(dimethylsiloxane) (PDMS) one of the most commonly used materials for microfluidics-based microdevices. However, unlike other polymer materials commonly used for microdevices, the PDMS cannot be easily etched or further changed upon polymerization, and therefore, fabrication method has been rather limited to replication molding. Here, we demonstrated liquid-phase capillary etching of the PDMS microchannels with tetra-n-butylammonium fluoride (TBAF) and characterized its etching profiles depending on the initial microchannel widths, TBAF flow rates, TBAF concentrations, and substrates used for the microfluidic channel sealing. The characterization showed that the microchannel circumference etch rate was linearly proportional to the TBAF flow rate and was faster at higher TBAF concentration. On the other hand, influence of the TBAF concentration on the horizontal and vertical etch rates was vastly different, with the vertical etch rate being much more affected by the concentration change. Potential applications of the liquid-phase capillary etching method were demonstrated by fabricating the PDMS microchannels with round-shaped cross sections, a microdevice with embedded 3-D metal electrodes with the electrodes directly exposed to the microfluidic channel, and a glass-PDMS-glass sandwich microchannel for high-clarity optical detection. We believe that the characterization of the liquid-phase capillary etching along with the applications demonstrated here will provide new capabilities for fabricating the PDMS-based microdevices that could not be easily fabricated by conventional replication molding processes.